2. Mutual Inductance:
Transformers are constructed of two coils placed so that the
charging flux developed by one will link the other.
The coil to which the source is applied is called the primary coil.
The coil to which the load is applied is called the secondary coil.
Three basic operations of a transformer are:
Step up/down
Impedance matching
Isolation
3. When two coils are placed close to each other, a changing flux in one coil will
cause an induced voltage in the second coil. The coils are said to have mutual
inductance M, which can either add or subtract from the total inductance
depending on if the fields are aiding or opposing.
Mutual inductance is the ability of one inductor to induce a voltage across a
neighboring inductor
5. Mutual inductance M21 of coil 2 ,with respect to coil 1.
Mutual inductance of M12 of coil 1 with respect to coil 2.
6. •Mutual inductances M12 and M21 are equal.
• They are referred as M.
• We refer to M as the mutual inductance between two coils.
• M is measured in Henry’s.
• Mutual inductance exists when two coils are close to each other.
• Mutual inductance effect exist when circuits are driven by time
varying sources.
• Recall that inductors act like short circuits to DC.
12 21
M M M
7. Dot Convention:
If the current ENTERS the dotted terminal of one coil, the
reference polarity of the mutual voltage in the second coil is
POSITIVE at the dotted terminal of the second coil .if the
current LEAVES the dotted terminal of one coil, the
reference polarity of the mutual voltage in the second coil is
NEGATIVE at the dotted terminal of the second coil
8.
9. Coils in Series
a) Series-aiding connection.
L=L1+L2+2M
b) Series-opposing connection.
L=L1+L2-2M
11. 1 2
1 1 1 1
2 1
2 2 2 2
1 1 1 1 2
2 1 2 2 2
TimeDomain
Frequency Domain
( )
( )
di di
v i R L M
dt dt
di di
v i R L M
dt dt
V R j L I j MI
V j MI R j L I
